1. Field of the Invention
The present invention relates to a stretch wrapping film. More particularly, it relates to a stretch wrapping film having excellent heat resistance, flexibility, mechanical strength, transparency, cuttability and original-shape resuming properties, which is used for stretch-packaging food alone or together with a plastic tray loaded therewith or the like.
2. Description of the Related Art
As stretch wrapping films for stretch-packaging food (e.g. fruits, vegetables, fresh fishes, fresh meat, daily dishes, etc.) alone or together with a plastic tray loaded therewith or the like, vinyl chloride resin films have been mainly used. Recently, to solve the problems concerning safety and sanitation (e.g., preventing the generation of carcinogenic substances by incineration), films of polyethylene type resins such as low-density polyethylenes, ethylene-vinyl acetate copolymers, etc. have been energetically developed in place of conventional vinyl chloride resin films.
However, when a low-density polyethylene or the like is used alone, it has been impossible to attain, for example, a good balance between the uniformity of film in elongation, film rigidity, and other desirable properties. The ethylene-vinyl acetate copolymer films are free from the above-mentioned problem in the low-density polyethylene films when the content of repeating units derived from vinyl acetate, the molecular weight, etc. are properly chosen. They, however, have been disadvantageous in being torn off to be broken in the case of packaging a tray having sharp corners or a food having a sharp-edged portion.
Therefore, for example, JP-B-2-12187 and JP-B-2-18983 have proposed stretch wrapping films obtained by laminating an ethylene-vinyl acetate copolymer on an ethylene-.alpha.-olefin copolymer in order to satisfy all the required performance characteristics at a time. Although these films are excellent in mechanical strength, they are poor in flexibility and original-shape resuming properties. Moreover, they are disadvantageous in that they are perforated when heat-sealed at the bottom of a tray due to their low heat resistance.
Accordingly, for example, JP-A-5-147174 has proposed a film obtained by laminating an ethylene resin on a layer of a mixture of a crystalline olefin resin and an olefin elastomer. JP-A-6-927 has proposed a film obtained by laminating an ethylene resin on a layer of a resin composition containing an amorphous polyolefin and a crystalline polypropylene.
Although these films are excellent in original-shape resuming properties, they have too high a resilience. Therefore, when a plastic tray loaded with food is packaged in the film with an automatic packaging machine, the film is turned in due to the resilience, so that the packaging machine is stopped.